Method and device for producing a foundation element in the ground

ABSTRACT

The invention relates to a method and to a device for creating a foundation element in the ground, wherein ground material is removed by means of a drilling tool and a borehole is created, into which a pile pipe and a curable medium are introduced. The borehole is created having a boring diameter that is greater than an outside diameter of the pile pipe by a specified amount, wherein an annular space is formed between a borehole wall and an outer face of the pile pipe. The removed ground material is conveyed in an interior of the pile pipe, while the annular space is kept substantially free of removed ground material. The curable medium is introduced into the annular space in order to anchor the pile pipe in the ground.

The invention relates on the one hand to a method for producing a foundation element in the ground, in particular in the bed of a body of water, in which ground material is removed by means of a drilling tool and a borehole is produced, into which a pile tube and a hardenable medium are introduced, in accordance with the preamble of claim 1.

The invention furthermore relates to a device for producing a foundation element in the ground, comprising a drilling means with a drilling tool for removing ground material below the pile tube which can be introduced into the ground as part of the foundation element, in accordance with the preamble of claim 10.

A generic method and a generic device can be taken from EP 2 322 724 A1. By means of an underwater drilling arrangement a pile-shaped foundation element is introduced into the bed of a body of water. On the tubular foundation element a drilling means is fixed which removes ground below the tubular foundation element and produces a borehole. The removed ground material can be pumped out of the tubular foundation element and a settable suspension can be introduced into the tube.

The load-bearing capacity of such a foundation element depends to a considerable degree on the skin friction with respect to the surrounding ground. Particularly in the case of a bed of a body of water this may result in a relatively low friction factor so that the foundation element has to be introduced into the ground at a corresponding depth and thus in a laborious manner.

From WO 2010/015799 A2 a method for underwater foundation can be taken, in which a borehole is produced initially. Into this a foundation tube with a smaller diameter can be introduced which is embedded on its internal and external face into a hardenable cement mass. This cement mass then hardens together with the tube element to form the foundation element.

In the described method the removed ground material is ejected from the borehole into the surrounding water. This can constitute an environmental impact. Moreover, a large amount of cement mass is required to form the foundation element. The handling of large amounts of cement underwater can also lead to an undesirable environmental impact.

The invention is based on the object to provide a method and a device for producing a foundation element in the ground, in particular in a bed of a body of water, with which a foundation element with a high load-bearing capacity can be produced efficiently and at the same time in an environmentally friendly manner as possible.

The object is achieved on the one hand by a method having the features of claim 1 and on the other hand by a device having the features of claim 10. Preferred embodiments of the invention are stated in the respective dependent claims.

The method according to the invention is characterized in that the borehole is produced with a drilling diameter which is, by a specified amount, larger than an external diameter of the pile tube, wherein an annular space is formed between a borehole wall and an external face of the pile tube, in that the removed ground material is conveyed into an internal space of the pile tube while the annular space is kept substantially free of removed ground material, and in that the hardenable medium is fed into the annular space in order to anchor the pile tube in the ground.

The invention is based on the finding that in order to achieve a high load-bearing capacity the foundation element is anchored in the surrounding ground by means of a hardenable medium, in particular a cement mass. To obtain this high load-bearing capacity is it not vital that the entire pile tube is filled with the hardenable medium or mass. In fact, the hardenable medium is substantially only fed into the external annular space formed between the external face of the pile tube and the borehole wall of the borehole that is larger by a defined amount. As a result, a connecting shell is formed that anchors the pile tube in the surrounding ground with a high friction factor. The consumption of hardenable medium can thus be reduced considerably which is on the one hand economical and on the other hand environmentally friendly. On completion of the method hardenable medium can be fed into the base area of the pile tube, whereby a stable pile base is formed. A central area located above preferably remains free of hardenable medium.

In this process, the ground material removed by the drilling tool does not have to be discharged completely from the borehole. In fact, it is possible that at least a part of the removed ground material remains inside the pile tube. Within the meaning of the invention the drilling tool is to be understood not only as a drilling tool driven in a rotating manner but, in principle, also as a cutter-like drilling tool, a drilling tool effecting removal through high-pressure injection, a combination of these drilling tools or another ground-removing tool.

A preferred embodiment of the method according to the invention resides in the fact that the removed ground material is mixed with a fluid, in particular water, which is fed into a lower area of the borehole. If the removed ground material is adequately liquefied through crushing and mixing with a liquid it can largely rise upwards inside the pile tube without additional conveying means, such as a conveyor flight. Basically, it is also possible that the ground material thus put into a flowable state is pumped away by a pumping means. In certain cases the fluid can also contain a hardenable medium.

In this process, it is preferred that the removed and mixed ground material is conveyed at least partially through the pile tube out of the borehole. Insofar as permitted and environmentally compatible, in underwater drilling the ground material can be released via a discharge piece into the surrounding water. By way of a corresponding line the removed ground material can also be conveyed ashore or to a vessel. In this connection it is of advantage that the removed ground material is not contaminated with the hardenable medium. This permits an easy disposal.

According to a preferred embodiment provision is made in that the drilling tool is driven in a rotating manner by means of a drill rod which is arranged inside the pile tube, and in that via the drill rod fluid is fed into the lower area of the borehole and/or removed ground material is discharged from the borehole. For this purpose, a hollow drill rod can be used that has one or several outlet openings in its lower area for the supply of a fluid, more particularly water. The fluid can also be supplied under pressure, thereby contributing to the ground removal and/or the mixing of the removed ground material.

Furthermore, according to an embodiment variant of the invention provision is made in that the hardenable medium is fed into a lower area of the annular space. To this end, one or several supply lines can be provided along the pile tube, in particular along the internal face of the pile tube. These lines lead into a lower area of the annular space so that the annular space produced can be filled up from below with the hardenable medium, more particularly a cement mass.

Provision can also be made for further openings around the circumference of the pile tube and along the axial height of the pile tube. The pile tube is, on the whole, designed with a lower annular shoulder such that the annular space is sealed tightly against the internal space of the pile tube, in which the removed ground material is accommodated. In this way, it prevents contamination of the internal removed ground material with the hardenable medium. At the same time, the hardenable medium is used sparingly and efficiently to fill the annular space. It should be noted that ground material can infiltrate from the borehole wall or to a certain extent also from the borehole bottom into the annular space or that such an infiltration can, at least, never be completely ruled out. However, from a quantitative viewpoint the hardenable medium is supplied to such an extent that even if ground material infiltrates, a sufficient hardening of the anchoring shell around the pile tube is reached. Of major importance is the fact that the hardenable medium cannot infiltrate into the interior of the pile tube and thus lead to an undesirable contamination of the removed ground material in the internal space of the pile tube.

A particularly efficient method is attained according to the invention in that the introduction of the pile tube, the removal of the ground material, the feeding-in of the fluid and/or the feeding-in of the hardenable medium take place simultaneously. All in all, a rapid sinking of the borehole and a speedy construction of the foundation element can thus be achieved.

Furthermore, according to an embodiment of the invention it is preferred that for removal of ground material inside the pile tube a drilling means is secured on the pile tube which has a drive means for driving the drilling tool in a rotating manner. The drilling means capable of being secured on the pile tube can have a support frame for example which can be secured by tensioning or clamping means on the pile tube and in which a drive means or a rotation motor for driving a drill rod is accommodated. The drilling means can be secured, for example, inside an internal cross section of the pile tube, thereby allowing the drilling means and the pile tube to be sunk jointly. It is also possible to provide a telescopic drill rod or to support the drill rod in an axially adjustable manner with respect to the support frame so that an independent axial feed motion of the drilling tool and the pile tube can take place.

According to the invention an especially economical method variant is attained in that after anchoring the pile tube in the ground, removed ground material remains inside the pile tube. Hence, the removed ground material is not or not entirely discharged from the pile tube. In fact, the removed ground material which can be crushed and, as the case may be, mixed with liquid remains inside the pile tube. Solidification of this material filling is not necessary since the load-bearing capacity of the foundation element primarily depends on the skin friction. In this way, the costs for the discharge of the ground material and an environmental impact possibly involved therewith can be avoided. Since the ground material is not contaminated with hardenable medium it does not constitute an environmental impact e.g. on underwater foundation elements even in the long term.

To produce the borehole with a larger diameter a specific drilling tool with radially extendable removal teeth can basically be used. Such a drilling tool can be folded in radially after sinking of the borehole and withdrawn upwards through the pile tube with a smaller diameter. With regard to the use of cost-intensive special-purpose vessels for underwater drilling operations an economical alternative resides in the fact that after sinking of the borehole the drill rod is separated from the drilling tool at the lower end of the pile tube, wherein the drilling tool remains in the ground as a lost drilling tool. Hence, a simple inflexible drilling tool can be used which remains in the ground as a lost drill bit on the underside of the foundation element.

The object stated at the beginning is furthermore achieved by a device which is characterized in that for the production of a borehole the drilling tool is designed with a drilling diameter which is, by a specified amount, larger than an external diameter of the pile tube, wherein an annular space is formed between the borehole wall and an external face of the pile tube, in that the annular space is separated from the interior of the pile tube, and in that the supply means for a hardenable medium is provided, wherein the supply means leads into the annular space. With this device the afore-described method can be carried out and the stated advantages can be accomplished.

Due to the continuous tube body of the pile tube and in particular due to an enlarged diameter, for instance by way of a shoulder, at the lower end of the pile tube the annular space on the external face of the pile tube is separated, as far as the process is concerned, from the interior of the pile tube. In this way, the achievement is made that no hardenable medium can pass from the external annular space into the interior of the pile tube. Likewise, ground material can also be prevented from infiltrating into the annular space. However, this poses no problem as long as the strength of the formed connecting mortar in the annular space is not significantly affected. Through a clear separation an efficient use of the hardenable medium in the annular space and the avoidance of contamination of the removed ground material in the interior of the pile tube are ensured. The supply means leads solely into the annular space but not into the interior of the pile tube.

Basically, the drilling tool can be operated in a conventional manner by a drilling device located outside the borehole, for instance on a drilling vessel. According to the invention it is preferred that the drilling means has a rotary drive for driving the drilling tool in a rotating manner and that the drill drive is designed for introduction into the pile tube and for being secured in the pile tube. By way of a suitable tensioning means the drill drive can be secured inside the pile tube. The drilling means can also be part of an underwater drilling unit that can be lowered into the body of water.

According to a further embodiment of the invention provision is made in that the drilling tool is driven in a rotating manner via a drill rod by the drill drive and in that between the drilling tool and the drill rod a mixing means is provided for crushing and/or mixing the ground material removed by the drilling tool with a supplied fluid, in particular water. The drilling tool and the mixing means can be operated simultaneously and can in particular be driven in a rotating manner. The supply of the hardenable medium takes place simultaneously with the operation of the drilling tool. Moreover, with the removal of ground material and the corresponding axial feed motion of the drilling tool the pile tube is also lowered into the ground. The mixing means can have mixing paddles or mixing blades that additionally crush the removed ground material and mix it with a supplied fluid so that the removed ground material reaches an overall flowable state.

In particular, the mixing means can also have eccentrically arranged mixing elements, whereby the mixing and crushing effect can be enhanced.

In the following the invention is described further by way of preferred embodiments illustrated schematically in the drawings, wherein show:

FIG. 1 a schematic side view of a device according to the invention;

FIG. 2 a longitudinal section of the device of FIG. 1;

FIG. 3 an enlarged cross-sectional view according to section A-A of FIG. 1; and

FIG. 4 an enlarged detailed illustration of the lower area according to FIG. 2.

According to FIGS. 1 and 2 a device 1 pursuant to the invention has a pile tube 10 which is substantially formed of a cylindrical base body 12. At the lower end of the cylindrical base body 12 a sleeve-shaped shoulder 16 with a larger diameter is designed which accommodates a mixing space 18.

Inside an internal space 14 of the pile tube 10 a drilling means 50 is arranged. The drilling means 50 can be clamped against the internal face of the pile tube 10. The pile tube 10 itself can be arranged in a known manner on a drilling unit, more particularly an underwater drilling unit. By way of the drilling unit, not shown, the pile tube 10 can be driven in a torque-proof or also in a rotating manner. During operation of the drilling means 50 the pile tube 10 is stationary and, once a section of the borehole has been produced, it can then be moved axially downwards into the borehole.

From the drilling means 50 a drill rod 26 extends axially downwards to the free end of the pile tube 10. Below the pile tube 10 a drilling tool 20 is arranged on the drill rod 26. The drilling tool 20 has a conveyor flight 24, at the lower end of which, starting from a central pilot bit 22, several radially arranged removal teeth 23 are located along cutting edges.

Between the drilling tool 20 and the drill rod 26 a mixing means 40 is interposed which is explained in greater detail hereinafter in conjunction with FIGS. 3 and 4.

The drill rod 26 has an inner drive shaft 28 and an outer drive shaft 38 surrounding the latter concentrically. The inner drive shaft 28 is driven in a rotating manner by a rotary drive 54 of a drive means 52, whereby the torque is transmitted from the inner drive shaft 28 to the drilling tool 20. Independent of this, the outer drive shaft 38 can be driven by a mixing drive 56 with a different direction of rotation and/or rotational speed. At the lower end of the outer drive shaft 38 a mixing means 40 is provided, through which removed ground material is mixed with supplied fluid.

Furthermore, the inner drive shaft 28 and the outer drive shaft 38 can be designed as hollow tube elements so that these can be used for introducing a fluid into the borehole, as will be set out in detail hereinafter.

By means of the drilling tool 20 a borehole with a drilling diameter is produced which approximately corresponds to the external diameter of the sleeve-shaped shoulder 16 at the lower end of the pile tube 10. In this way, the pile tube 10 can be followed down into the borehole without any considerable amounts of removed ground material being able to flow past the external circumference of the sleeve-shaped shoulder 16 in the upward direction.

Compared to the sleeve-shaped shoulder 16 with a larger diameter the cylindrical base body 12 of the pile tube 10 has a smaller diameter so that an annular space 8 is formed between the external face of the cylindrical base body 12 and a borehole wall 5. By way of a supply means 30 a hardenable medium, in particular a cement mass, can be fed into the annular space 8 that can be filled therewith. For this purpose, the supply means 30 has a line 32 that extends from a pump, not shown, along an internal face of the cylindrical base body 12 of the pile tube 10. By way of an elbow 34 the supply line 32 leads into the annular space 8, as can be taken from FIG. 4 in particular.

With reference to FIGS. 3 and 4 the lower end area of the device 1 and the pile tube 10 is described in greater detail. Via a radial annular plate 17 the sleeve-shaped shoulder 16 is connected in a fluid-tight manner to the external circumference of the cylindrical base body 12 of the pile tube 10. As a result, the annular space 8 formed between the borehole wall 5 and the external circumference of the continuous cylindrical base body 12 is sealed off tightly against an internal space 14 of the pile tube 10.

Below the sleeve-shaped shoulder 16 the drilling tool 20, having the same external diameter, is arranged with conveyor flights 24 and a pilot bit 22. The drilling tool 20 is driven in a rotating manner by the inner drive shaft 28. Ground material is removed and conveyed upwards by the conveyor flights 24 into a mixing space 18 designed inside the sleeve-shaped shoulder 16. In the mixing space 18 a mixing means 40 is arranged. In the illustrated embodiment the mixing means 40 comprises three plate-shaped inner mixing elements 42 which are arranged at the same angular distance in relation to each other and are mounted on the inner drive shaft 28 so as to rotate therewith.

Moreover, the mixing means 40 comprises three plate-shaped outer mixing elements 44 which are also arranged such that they are offset by 120° in relation to each other and are connected in a torque-proof manner to the outer drive shaft 38. An outer mixing element 44 has an upper radial bar 46 and a lower radial bar 47 which are firmly connected to each other by way of an axial connecting element 45. The lower radial bar 47 is supported in a rotatable manner with respect to the inner drive shaft 28. On an internal face of the connecting element 45 a radially inward projecting shear plate 48 is arranged.

Through a relative rotation of the inner mixing elements 42 and the outer mixing elements 44, which rotate in opposite directions in particular, the removed ground material conveyed by the conveyor flights 24 is crushed further and mixed with liquid that is fed via fluid lines 58 in the interior of the drill rod 26. The fluid lines 58 are in particular arranged in the intermediate space between the inner drive shaft 28 and the outer drive shaft 38 and have laterally-directed radial outlet openings as well as downward-directed ones for the injection of liquid. At the same time, liquid can be fed directly downwards via the remaining annular space between the two drive shafts. The mixing and liquefying of the removed ground material is additionally enhanced by a radially inward projecting annular protrusion 60, through which the removed ground material is forced radially inwards into the mixing space 18. Through the effect of the conveyor flights 24 and the supply of liquid the ground material thus crushed and mixed is displaced upwards into the internal space 14 of the pile tube 10.

Separated tightly from the internal space 14 is the annular space 8 between the borehole wall 5 and the cylindrical base body 12. Basically, the separation of these two process spaces can be enhanced further in that the pressure in both process spaces is controlled by controlling the respective filling levels. Via the supply line 32 and the elbow 34 a hardenable medium is fed into the annular space 8 at the lower end thereof. The hardenable medium, in particular a cement mass, hardens after sinking of the borehole and introduction of the pile tube 10 into the borehole so that a solid connecting shell is created thereby between the borehole wall 5 and the pile tube 10 so as to form the foundation element.

A pressure in the internal space 14 can be controlled via a filling level of the removed and mixed ground material in the internal space 14. In particular, the filling level can be set by means of a pump, not shown. Basically, the pressure in the internal space 14 can be higher than in the annular space 8, whereby a leakage of the hardenable medium from the annular space 8 into the internal space 14 is prevented in a particularly reliable manner. This ensures that the removed ground material in the internal space 14 is not contaminated with hardenable medium thus necessitating its disposal at high costs. By preference, the pressure in the annular space 8 is higher than in the internal space 14, whereby an infiltration of ground material into the annular space 8 is counteracted.

After the connecting shell in the annular space 8 has hardened, crushed and/or liquefied ground material can remain in a non-hardened state in the internal space 14 of the pile tube 10. For, even in the case of an underwater foundation, the loosened ground material, which is not contaminated with hardenable mass, does not constitute an environmental impact. To form the foundation element the pile tube 10 and the drilling tool 20 remain in the ground while the drill rod 26 is recovered together with the mixing means 40. 

1. Method for producing a foundation element in the ground, in particular in a bed of a body of water, in which ground material is removed by means of a drilling tool (20) and a borehole is produced, into which a pile tube (10) and a hardenable medium are introduced, characterized in that the borehole is produced with a drilling diameter which is, by a specified amount, larger than an external diameter of the pile tube (10), wherein an annular space (8) is formed between a borehole wall (5) and an external face of the pile tube (10), in that the removed ground material is conveyed into an internal space (14) of the pile tube (10) while the annular space (8) is kept substantially free of removed ground material, and in that the hardenable medium is fed into the annular space (8) in order to anchor the pile tube (10) in the ground.
 2. Method according to claim 1, characterized in that the removed ground material is mixed with a fluid, in particular water, which is fed into a lower area of the borehole.
 3. Method according to claim 2, characterized in that the removed and mixed ground material is conveyed at least partially through the pile tube (10) out of the borehole.
 4. Method according to claim 1, characterized in that the drilling tool (20) is driven in a rotating manner by means of a drill rod (26) which is arranged inside the pile tube (10), and in that via the drill rod (26) fluid is fed into the lower area of the borehole and/or removed ground material is discharged from the borehole.
 5. Method according to claim 1, characterized in that the hardenable medium is fed into a lower area of the annular space (8).
 6. Method according to claim 1, characterized in that the introduction of the pile tube (10), the removal of the ground material, the feeding-in of the fluid and/or the feeding-in of the hardenable medium take place simultaneously.
 7. Method according to claim 1, characterized in that for removal of ground material inside the pile tube (10) a drilling means (50) is secured on the pile tube (10) which has a drive means (52) for driving the drilling tool (20) in a rotating manner.
 8. Method according to claim 1, characterized in that after anchoring the pile tube (10) in the ground, removed ground material remains inside the pile tube (10).
 9. Method according to claim 4, characterized in that after sinking of the borehole the drill rod (26) is separated from the drilling tool (20) at the lower end of the pile tube (10), wherein the drilling tool (20) remains in the ground as a lost drilling tool (20).
 10. Device for producing a foundation element in the ground, in particular according to claim 1, comprising a drilling means (50) with a drilling tool (20) for removing ground material below a pile tube (10) which can be introduced into the ground as part of the foundation element, characterized in that for the production of a borehole the drilling tool (20) is designed with a drilling diameter which is, by a specified amount, larger than an external diameter of the pile tube (10), wherein an annular space (8) is formed between the borehole wall (5) and an external face of the pile tube (10), in that the annular space (8) is separated from the interior of the pile tube (10) and in that a supply means (30) for a hardenable medium is provided, wherein the supply means (30) leads into the annular space (8).
 11. Device according to claim 10, characterized in that the drilling means (50) has a rotary drive for driving the drilling tool (20) in a rotating manner and in that the rotary drive (54) is designed for introduction into the pile tube (10) and for being secured in the pile tube (10).
 12. Device according to claim 11, characterized in that the drilling tool (20) is driven in a rotating manner via a drill rod (26) by the rotary drive (54) and in that between the drilling tool (20) and the drill rod (26) a mixing means (40) is provided for crushing and/or mixing the ground material removed by the drilling tool (20) with a supplied fluid, in particular water. 